1. Field of the Invention
The invention is related to the field of fluid systems, and more particularly, to filters.
2. Description of the Prior Art
Equipment may employ fluids such as clean dry air (CDA) to perform various functions in different industries. In the rail industry, rail cars may employ CDA to operate pneumatic systems. The pneumatic systems may control parts that perform the various functions on the rail cars. For example, the pneumatic system may control brakes to stop the rail car. In the semiconductor industry, manufacturing equipment may employ pressurized CDA to operate valves to open and close ports. For example, multi-chamber wafer processing equipment may employ the ports to isolate each chamber from a central platform while still allowing a robot on the central platform to place and remove a wafer in the chamber. These are just exemplary industries and do not limit the scope of this application.
It is desirable that the CDA (or other appropriate fluid) not adversely affect the parts in the equipment. To ensure that the CDA does not adversely affect the parts, the CDA should be substantially free of moisture and other undesirable components such as particulates. CDA that is free of moisture and other undesirable components is less likely to cause corrosion or other adverse effects on the pneumatic system or components. For example, particulates may be abrasive to moving components, such as valves, in the pneumatic system. Reducing the adverse effects on a pneumatic system may extend the operating life of the pneumatic system.
Filters are often employed to remove one or more components from the fluid. For example, filters may remove moisture from compressed air to provide CDA to the pneumatic system. Also, filters may be employed by the equipment that uses the CDA because it may not be feasible to store CDA. More specifically, the filter receives compressed air from a source, filters the air and provides CDA to the equipment as the equipment requires (e.g., when the pneumatic system is controlling the equipment). Sometimes, the equipment will take and compress air from the environment and provide it to the filters. The filters may include material that adsorbs moisture from the compressed air provided by the equipment. In filters, desiccant beads or membranes are employed to adsorb the moisture from the air. Although this discussion is directed to removing moisture from air by adsorption, the filters may employ any appropriate means of removing any components from a fluid needed by the equipment. By employing the filters, the equipment may obtain CDA while in operation.
However, the filters may have undesirable characteristics. For example, operating ranges of the filters may be undesirably narrow. In particular, the filtering media in the filters may require a narrow fluid flow rate which may render the filtering media unsuitable for equipment that may require a wide range of fluid flow rates. A wider operating range for the filters would allow a filter to be used in a larger variety of equipment.
The filters may also require frequent planned maintenance. For example, the filters may require replacement more frequently than the other parts in the equipment. In other words, the frequency of the planned equipment downtime may be dictated by the filters rather than the parts in the equipment. Also, the filters may not reliably adsorb moisture from the air unless the filters are oriented in a desired manner. For example, in filters that employ desiccant beads, the air may bypass the desiccant beads if the filters are not oriented vertically. This may prevent use of the desiccant bead filters in equipment that changes orientation during operation.
It has also been found that the filters may be prone to failure thereby causing unexpected equipment downtime. For example, the filters may become unexpectedly saturated with moisture. The saturation may cause an undesirable pressure drop or increase in the amount of moisture in the CDA provided to the equipment. Unexpected pressure drops in the CDA supplied by the filter can cause the pneumatic system to cease functioning thereby causing parts in the equipment to not function. In filters that employ desiccant beads, the beads may be prone to degrading and creating particulates due to vibration of the beads. The particulates may be carried by the CDA to the equipment. The particulates may also obstruct the air flow through the filter.
Equipment downtime, particularly downtime associated with sophisticated equipment automated by pneumatic systems, is very costly. For example, rail cars not being used to transport cargo while filters are being replaced may have opportunity costs that range from hundreds to several thousands of dollars an hour. Even seemingly modest improvements in reducing equipment downtime can result is considerable savings when the same improvements are employed over hundreds or thousands of similarly situated pieces of equipment. Moreover, unexpected downtime of the equipment may result in large scale disruptions such as shutting down a manufacturing facility or rail systems. Hence, significant financial benefits may be realized by reducing equipment downtime.
What is needed, therefore, is a more reliable filter.